This invention relates to combustion heaters and, in particular, to gas fired pulse combustion space heaters.
The development of suitable pulse combustion furnaces has enabled the advantages and efficiencies of pulse combustion to be attained in residential central heating. In addition to the advantages of self-sustaining operation, the steady state thermal efficiency of such central heating systems may be higher than 90% and provide significant operating cost savings. There is a need for a pulse combustion fired space heater to provide comparable advantages and thermal efficiencies.
The development of a suitable space heater involves restrictive size and noise suppression requirements since space heaters are not typically isolated in a basement or closet as in the case of a central heating furnace. For a heater capacity of about 20,000 BTU/hr. to be used in residential applications, the compact size requirements of commercially sized space heaters require that the overall size of the appliance be about 3 feet wide, 2 feet high and 1 foot deep. The sound level of the unit at a distance of three feet should be about 53 dBA or less.
The imposition of size requirements, especially the relatively compact dimensions contemplated herein, are particularly difficult to meet in pulse combustion systems since the resonant operation thereof requires certain geometric configurations and/or size relationships to be observed. More particularly, in pulse combustion burners of the Helmholtz type, an oscillating or pulsed flow of combustion gases through the burner is maintained at a frequency determined by burner component geometry and fuel supply characteristics. Typically, a combustion chamber of a given size cooperates with a tailpipe or exhaust pipe of specific dimensions to provide explosive combustion cycles, thermal expansion of the combustion gases, and oscillating gas pressures which provide a pulsed flow of combustion gases through the burner. In order to make the pulse combustion process self-sustaining, the oscillating gas pressures may be used to provide self-feeding of a combustible gaseous mixture. Accordingly, the close relationship between pulse combustion operation and heater geometry restricts variation in the spatial arrangement and compaction of the heater elements to meet commercial size requirements. It is also necessary to achieve efficient heat transfer with the air to be conditioned.